Process for producing magnesium



Patented July 24, 1934 PROCESS FOR PRODUCING MAGNESIUM Pierre Camescasse, Paris, France, assignor to The Magnesium Production Co. Ltd, London, England Application April 14, 1930, Serial No. 444,2

In Germany 24, 1929 8 Claims. (Cl. 204-19) The present invention relates to an improved process for the electrolytic manufacture of magnesium, in which the electrolyte consists of a mixture of magnesium chloride and potassium chloride or carnalite.

In the known processes of this class, measures are taken, as specified in the copending patent application, filed on the 5th of April 1929, Ser. No. 440,637, Lacell, to preliminarily dehydrate the magnesium chloride before it is placed in the electrolytic vat, and in order to/prevent all improper formation of oxides during this dehydration, to add to it chloride of potassium.

This method is defective owing to the fact that the electrolytic bath (to which are added frequently-renewed quantities of potassium chloride and in which the magnesium chloride is alone decomposed), will after a longer or shorter period of use, come to contain an excessively large proportion of potassium chloride, and it is impossible to maintain the optimum composition of the electrolyte.

The present invention relates to a process for the maintenance of the electrolyte at a practically constant composition. and for assuring in good conditions the addition of the potassium chloride used to further the dehydration of the magnesium chloride.

The process consists essentially in the removal from the electrolytic bath, when the proportion of KCl exceeds the proper value, of a certain amount of the bath, then mixingthis elctrolyte with the magnesium chloride which is undergoing dehydration.

The said electrolyte is preferably mixed with the partly dried magnesium chloride at some stage of the drying, in which the temperature is sumciently high to provide for an instantaneous and intimate mingling. The removed electrolyte is added to such a quantity of chloride of magnesium that when the drying is completed, there remains a mixture of substantially equimolecular proportions of magnesium chloride and potassium chloride. However, in this mixture, the proportion of MgClz can be as high as 10 molecules of MgClz to 8 molecules of KCl. The reaction will still take place, although imperfectly, as far as 10 molecules MgCh to 5 molecules of KCl.

It should be noted that when thus proceeding, the potassium chloride follows a closed cycle, and that when the manufacture is proceeding under normal conditions, no further additions of KCl are needed, except to make up for the small losses.

The process is described as follows by way of example which is given as illustrative, without limiting the invention thereto.

The electrolysis takes place with the use of a mixture whose proportion is kept at about 70 per cent of KCl to 30 per cent of MgClz. The vat is supplied with a mixture of per cent of MgClz and 40 of KCl, which product is obtained by mixing the electrolyte taken from the vat with magnesium chloride (containing 41120) in the proportion of 42 per cent of the said electrolyte to 58 of melted magnesium chloride (containing about 4 molecules of water).

It has further been observed by the applicant that the best results are afforded for the dehydration by using a mixture whose composition comes near that of carnalite, that is, 60 per cent of MgClz to 40 of KCl, and hence the operator will choose the quantities of electrolyte taken from the bath and the quantity of partly dehydrated magnesium chloride to which the same is added, so as to practically maintain this proportion.

The portion of the electrolyte removed from the electrolytic cell may be added during one or the other steppi the dehydration or before the dehydration. It is recognized that the drying takes place preferably in successive steps, in which the magnesium chloride, hydrated to the extent of 6 molecules of water, is first melted, is then held in the molten condition until it contains 4 molecules of water, and is then completely dehydrated by a subsequent operation, employing for instance the process specified in the said copending application made by Eliza Lacell executrix of Harold George Lacell No. 440,637. These three operations are designated as (a) (b) and (c) in the accompanying drawing. It is pos sible to operate in any of the four following manners;

(1) When the operator adds the mixture taken from the electrolytic vat to the magnesium chloride before the beginning of the dehydration according to the cycle t he cools and dissolves the mixture and then mixes it with the solution of magnesium chloride. Its apparent heat will be lost 'in such a process.

(2) He may add the mixture taken from the electrolytic vat to the molten magnesium chloride containing six molecules of water according to the cycle a: during its dehydration.

(3) He may, by taking certain precautions, mix it according to the cycle y with the melted chloride containing four molecules of water which is at about 250 C.

(4) According to the invention, but without ill fill

limitation thereto, it is round easier to add in the third dehydrating step in which there -is already a mass of practically anhydrous chloride, simultaneously the magnesium chloride containing four molecules of water obtained from operation (b) and the chloride mixture taken from the electrolyte.

I claim: v

1. Process 01' manufacture of metallic magmeslum by electrolysis of a mixture of the chlorides of magnesium and potassium consisting in maintaining an electrolytic bath of said fused chlorides in an electrolytic cell, withdrawing from said cell a portion oi the electrolyte rich in chloride oi potassium, adding to this portion while in a hot condition and without previously adding water thereto, magnesium chloride containing some water, to serve as the primary material to be electrolyzed, heating sufllciently to dehydrate the mixture thus obtained, and returning the so de hydrated mixture into the electrolytic cell.

2. Process of electrolysis for the production of metallic magnesium, which comprises maintaining in the electrolytic cell a mixture of chlorides of magnesium and potassium, withdrawing from the electrolytic cell a portion of theelectrolm rich in chloride of potassium, partially dehydrating chloride of magnesium serving as the primary material to be clectrolyzed, and adding this par= tially dehydrated chloride of esium to said portion so withdrawn, dehydrating the mixture thus obtained and returning the so dehydrated mixture to the electrolytic cell.

3. Process according to claim 2, in which the percentage oi chloride of potassium in the mixture so returned is about 49%.

i. Process of manufacture oi metallic magnesium by electrolysis of a mixture of chlorides of magnesium and potassium, consisting in maintaining a mixture oi said chlorides in the electrolytic cell, withdrawing i'rom said cell a portion of the electrolyte rich in chloride of potassium, simultaneously adding to said portion, partially de= hydrated chloride of magnesium, melting the mix tune to dehydrate the same, and returning said molten mixture into the electrolytic cell.

5. Process of manufacture of metallic magnesium by electrolysis of a mixture of the chicrides of esium and potassium consisting in maintaining a bath of said lused chlorides in an electrolytic cell, withdrawing from said cell a portion of the electrolyte rich in chloride of potassium, adding to this portion magnesium chloride containing some water, serving as the primary nonzero material to be electrolyzed, to dehydrate d e added slum chloride and form a substantially anhydrous mixture, and returning the mixture into the electrolytic cell.

6. A process of producing metallic esium by electrolysis ot a mixture containing magnesium chloride and potassium chloride, which comprises maintaining a bath consisting essentially 0! said chlorides in a fused state, in an electrolytic cell,

while passing an electric current through thesame sumcient to cause formation of metallic magnesium from magnesium chloride in said bath, and after a time, when the relative proportion oi esium chloride in said bath has been substantially reduced, withdrawing from said cell a portion of the electrolyte which has due to said electrolysis, become substantially enriched in potassium chloride, with this portion so withdrawn, a quantity oi material consisting essentially of magnesium chloride conta some water oi hydration, the relative amounts oi said materials so mixed being so adjusted that the heat of the mass is sufllcient to substantially dehydrate the added magnesium chloride, and to form a substantially anhydrous mixture consisting essentially of the two chlorides, which mixture is then brought into said electrolytic cell ior electrolysis therein. 7 4

7. Process of electrolysis for the production of metallic magnesium, which comprises maintaining in the electrolytic cell a molten substantially anhydrous e of chlorides of magnesium and potassium, withdrawing from the electrolytic cell a portion of the electrolyte rich in chloride of potassium, partially dehydrating chloride oi magnesium serving as the primary material to be electrolyzed, and mixing this partially dehydrated chloride of magnesium with said portion oi electrolyte so withdrawn while the latter is still molten, dehydrating the mixture thus obtained and returning the so dehydrated ure to the electrolytic cell.

8. Process of manufacture or meic mag-= nesium by electrolysis or a fused anhydrous mire ture of chlorides of magnesium and potassi, consisting in maintaining a mixture oi said chlo rides in the electrolytic cell,withdrawing from d cell a portion of the electrolyte rich in chloride of potassium, adding to said portion while molten, partiallly dehydrated chloride of magnesium, de= hydrating the mixture so formed, and as 1 he said dehydrated mixture into the electrolytic cell.

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